This invention relates to optical fiber connectors for use in optical communication systems and, more particularly, to a ferrule blank for making ferrules for use in such connectors.
In optical fiber communications arrangements, there has been a steadily increasing improvement in the reduction of signal loss within the fiber itself, but fiber signal loss is the major contributing factor to signal loss in long distance system which can be compensated for by the use of fiber amplifiers. An additional critical loss factor is the quality of the coupling when two signal bearing fibers are connected together, inasmuch as the junction between the two fibers represents a discontinuity where signal losses can, and do occur.
In general, fibers are connected together in end-to-end, butting relationship by means of connectors having fiber holding ferrules therein. It is common practice to finish the end of each ferrule in a generally flat surface normal to the axis of the fiber whereby the flat faces of the two ferrules involved in a connection bear against each other, and hence, the fiber ends abut, often with an index matching gel therebetween.
The present state of the art is such that, for various reasons, there exists a large number of connectors, or ferrule containing connector plugs, which differ from each other in one or more particulars, including the configuration of the fiber holding ferrule. Such a plethora of differing connector plugs makes it difficult to standardize connectors and their ferrules, thus requiring custom made ferrules that fit a particular connector but seldom meet the requirements of other connectors. For example, mating ferrules are generally inserted into alignment sleeves which are most often zirconia or metallic, and their pedestals abut each other within the sleeve. The term pedestal refers to that portion of the distal end of the ferrule that is polished for optimum mating with the abutting ferrule of the connector plug with which it forms a connection and includes angular bevels or chamfers. Most often, in the present state of the art, the end faces appear flat and parallel, but in most cases, the distal ends of the ferrules are domed by 7 to 25 mm, requiring, as an optimum, that the apex of the dome and the optical axis of the fiber contained within the ferrule coincide, an extremely difficult configuration to achieve. It has been found that an apex offset of something less than 50 xcexcm is acceptable. It has been proposed that the ferrule blank be made with a tapered distal end to produce a small diameter pedestal which may be ground with either a flat or domed configuration. Where the ground and polished end is flat the angle of the bevel or taper is preferably small so as to produce a relatively large pedestal, whereas when the distal end is to be domed, or, in some connectors, flat, the angle is large, resulting in a small surface area pedestal. Such a small area is difficult to polish with precision inasmuch as it tends to tear the polishing cloth or paper because of the high pounds-per-square inch forces thereon. On the other hand, a large bevel angle functions to guide the ferrules into the alignment sleeve without damaging it, whereas a shallow angle is less efficient as a guide and the ferrule is sometimes scraped as it enters the sleeve, resulting in damage to the ferrule or, possibly, the sleeve or sleeve holder. Too shallow an angle can also lead to problems of instability where too much of the length of the ferrule is tapered and not enough thereof is a slip fit within the alignment sleeve. As a consequence of the foregoing, the conflict between taper or bevel angles has forestalled efforts to standardize the ferrule blank. For example, a proposed ferrule blank having a bevel angle that represents a compromise between large and small angles has been submitted to the International Electrotechnical Commission (IEC), but has met with objections by connector manufactures and users, and thus has not yet been universally accepted for all SFFC (Small Form Factor Connectors).
Among the most widely used connectors are the LC type and the Mu type, but the dimensions of their ferrules, more particular, the pedestal dimensions, are so different that arriving at a standardized ferrule blank is seemingly a hopeless proposition, even for new SFFC designs such as the LX.5 by ADC and the F3000 by Diamond. For a variety of reasons, however, a standardized ferrule blank is greatly to be desired.
The present invention is a ferrule blank which can be adapted for use in a wide variety of differently configured connectors, and thus is amenable to standardization. Most particularly, the ferrule blank of the invention is usable with both the LC type and MU type connectors, as well as many other types of connectors.
The ferrule blank of the present invention has, at its distal, or pedestal, end a first bevel angle of approximately thirty degrees (30xc2x0) extending from the outer diameter of the ferrule, which is approximately 1.25 mm to a point where the diameter of the ferrule is approximately 0.90 mm, and a second bevel of forty to forty-five degrees (40xc2x0-45xc2x0) is formed which extends to the pedestal end. The ferrule blank has a diameter in the range of 0.60 mm to 0.75 mm approximately before polishing and a diameter in the range of 0.600 mm to 0.850 mm approximately after polishing. This equates to a total ferrule chamfer length of approximately 0.452 mm to 0.377 mm for a combined 30xc2x0 and 45xc2x0 angle prior to polishing, and approximately 0.452 mm to 0.327 mm after polishing. As will be apparent hereinafter, the ferrule of the invention, dimensioned as set forth in the foregoing, can be used, after appropriate grinding, with a wide variety of connector plugs from LC to Mu as extremes. There is no necessity for custom designing a ferrule for any of numerous connectors inasmuch as the operation of grinding the pedestal creates a butting surface at the distal end of a desired diameter and a ferrule end configured to fit most of the connector adapters containing an alignment sleeve.
Some manufacturers insist upon a forty to forty-five degree bevel angle for insuring proper guidance of the ferrule into the sleeve and which provides a relatively small bevel length, thereby insuring stability of the ferrule within the sleeve. However, as will be pointed out hereinafter, the pedestal diameter is relatively quite small, with the inherent disadvantage thereof. The second bevel (or chamfer) angle of the ferrule of the present invention substantially meets these requirements for guidance and stability even after grinding, as will be shown, and advantageously results in, after grinding, a greater pedestal diameter. Other manufacturers prefer a shallower bevel angle so as to produce a large diameter pedestal, and thus their ferrules are incompatible with the first group, and still other manufacturers seek a compromise between the two extremes. In virtually all cases, the ferrule blank of the present invention makes possible, with appropriate grinding, a finished ferrule that can satisfy the requirements of most manufacturers, thus eliminating the customized ferrule blank configuration by standardizing the ferrule blank configuration.
The principles and features of the present invention will be more readily apparent from the following detailed description, read in conjunction with the drawings.